# What the numbers do not say

The questions the measurements on this site cannot answer, and which metric to reach for instead of guessing.

Source: https://jmrplens.github.io/mikroscope/cost/limits/

Every measurement on this site was taken on one device, on one day, under one
load. This page is the list of things it therefore does not tell you — kept
here, in the documentation, rather than left for a reader to discover by being
wrong.

## What `/metrics` can recover, and what it cannot

The histogram `mikroscope_cpu_busy_ticks` (integer busy ticks per sample and core, which keeps
timing jitter out of the bucket choice) recovers **time above a threshold** to one sample. It cannot recover **contiguity**: a 2 s plateau at 30 % and twenty
scattered 100 ms spikes at 30 % look identical in it.

That is what `mikroscope_cpu_busy_run_seconds{threshold="0.5"|"0.9"}` is for —
the length of each run of consecutive samples at or above the threshold,
observed when the run ends, with the run still in progress in
`…_run_open_seconds`.

The trailing-window gauges (`window="1s"|"10s"|"60s"`, `stat="max"|"min"|"p95"`)
show the peak whatever your scrape interval is, because the agent computes them
over its own clock rather than over yours. To see the _shape_ of a transient
rather than its envelope, `record` it, or let a trigger capture it.

## The sampler's own smear is published, not hidden

How late the sampler woke after its ticker and how long the read took are
`mikroscope_tick_wake_latency_seconds` and `mikroscope_tick_read_seconds`, with
the interval actually achieved in `mikroscope_tick_interval_seconds`. If you
suspect the sampler rather than the router, those three are where to look
first.

## Gaps are reported, never papered over

The agent keeps 300 s by default. A collector outage shorter than that is
backfilled on reconnect through `since=<seq>`; a longer one is reported as a gap
of known length — a marker in a recording, a counter on the collector. A chart
with a hole in it is a chart telling the truth.

> **Not measured, so not claimed**
>
> Any board that is not the RB5009 described on [the rate ceiling](/mikroscope/cost/rate-ceiling/).
> Traffic heavier than about 30 Mbit/s. A 32-bit RouterOS build, which is
> coming on a hEX S but has not arrived. Sustained operation beyond the windows stated. None of
> these are claims this project is making, and none of them should be inferred from the ones it is.

## See also

- [The rate ceiling](/mikroscope/cost/rate-ceiling/): the five runs and the conditions they were
  taken under.
- [The cost of the observer](/mikroscope/cost/): the budget, and how to measure the cost on a device
  that is not this one.